Maintenance is an effective means to restore the technical performance of construction machinery, eliminate faults and hidden dangers and prolong the service life of machinery. At present, the domestic automobile maintenance industry has a considerable scale, while the construction machinery maintenance industry started late, and there are still many technical problems in maintenance. The existence of these problems leads to low quality of mechanical maintenance and poor reliability of equipment, which makes consumers suffer losses and even causes major construction machinery accidents. The author briefly analyzes the common technical problems encountered in the maintenance of construction machinery in order to attract the attention of relevant personnel. Xi' an engineering machinery specialist college
1. Failure can be correctly judged and analyzed, and blind disassembly is common.
Some maintenance personnel don't know the structure and principle of construction machinery, don't carefully analyze the cause of the failure, can't accurately judge the location of the failure, and blindly disassemble the machinery with the idea of "probably, almost". As a result, not only the original faults have not been eliminated, but also new problems have emerged due to poor maintenance skills and technology. 1 Nissan Komatsu bulldozer has the faults of insufficient diesel engine power and mechanical failure. The maintenance personnel disassembled and decomposed the PT fuel injection pump and fuel injector, but failed to find the cause of the failure. Replace 1 fuel injection pump for testing, and the fault still exists. Finally, the fault was caused by excessive impurities and moisture in the diesel oil used, but this disassembly led to a significant decline in the performance of the PT fuel injection pump and insufficient power of the diesel engine. Therefore, when the machinery fails, it should be detected by testing equipment. If there is no testing equipment, the most possible fault location can be determined by traditional fault judgment methods and means such as "asking, looking, checking and trying", combined with the structure and working principle of construction machinery. When judging the faults of construction machinery, the "exclusion method" and "comparison method" are commonly used, and they are carried out in the order from simple to complex, from appearance to interior, from assembly to parts, and it is forbidden to "disassemble indiscriminately". Xi' an engineering machinery specialist college
2. The phenomenon of blindly replacing parts and blindly "replacing parts for repair" exists to varying degrees.
It is relatively difficult to judge and eliminate the faults of construction machinery. Some maintenance personnel always use the replacement test method. Whether it is a big part or a small part, as long as it is considered that it may cause failure, it will be replaced one by one. As a result, the failure was not eliminated, and the parts that should not be replaced were replaced at will, which increased the expenses of consumers. 1 74 type II excavator was repaired in a factory, but it was useless for the factory to replace parts such as vane pump (steering pump), overflow valve and steering cylinder due to steering difficulties. Later, it was found that the fault was caused by the aging and peeling of a hydraulic oil pipe from the steering oil tank to the vane pump, resulting in insufficient hydraulic oil flow and pressure. There are also some faulty parts that can completely restore their technical performance through repair, such as generators, starters, oil coolers, gear oil pumps, etc. It can be repaired without complicated maintenance process, but the maintenance personnel ask users to replace new parts and blindly adopt the method of "replacing parts for repair", which causes serious waste. The above-mentioned blind replacement tests and repairable parts still exist in some repair units to varying degrees. When maintaining, we should carefully analyze and judge the cause and location of the fault according to the fault phenomenon, and restore the technical performance of the repairable parts by means of repair to prevent blind replacement of parts. Xi' an engineering machinery specialist college
It is common not to check the quality of new parts after assembly.
It is unscientific for some maintenance personnel to directly install new parts on construction machinery without technical inspection before replacing them. At present, the quality of spare parts sold in the market is uneven, and some fake and shoddy spare parts are true; There are also some accessories whose performance will change due to long storage time. If they are not tested, they usually lead to failure after assembly. 1 Shanghai 120A bulldozer, the oil cooler of diesel engine freezes and cracks, resulting in water in the oil. After replacing the new oil cooler and starting the trial operation, there was still water in the oil, and other parts were inspected, but the cause of the failure was not found. Xi' an engineering machinery specialist college
After disassembling the side cover of the new oil cooler, it was found that the oil seal ring at the side cover was not pressed tightly, resulting in oil-water mixing, because the quality of the oil cooler was not up to standard. 1 ZL50 loader, the oil pressure of diesel engine is too low. The analysis shows that the oil filter is blocked, and a new oil filter is replaced, but the oil pressure is still low. After checking or replacing all parts that may cause low oil pressure, the oil pressure still cannot rise. Finally, it was barely used when the cause of the failure was not found and the oil pressure was low. As a result, the diesel engine burned out the bearings, the crankshaft was broken and the connecting rod was bent, resulting in a loss of more than 10,000 yuan. After inspection, it is because the replaced oil filter element (coarse filter) has been blocked by too much rust, and the internal rust of the filter element is caused by long-term storage. Therefore, before replacing new accessories, it is necessary to carry out necessary inspections and tests, including appearance and performance tests, to ensure that the new accessories are trouble-free and eliminate unnecessary troubles. Xi' an engineering machinery specialist college
4. Not paying attention to the model of accessories, it is not uncommon for accessories to be replaced or misused.
In the maintenance of construction machinery, substitution or misuse of parts is still very common. Emergency substitution of some parts is feasible, but long-term use is harmful, affecting the safety and technical performance of machinery. Some maintenance personnel don't know much about the mechanical structure and principle, and many spare parts don't match the model, but they think that as long as they can be installed, they don't consider whether they can give full play to the technical performance of the machinery. For example, a 4 120F diesel engine should use a 350W generator, but it uses a 500W generator, which is a waste of power. ZL50 loader uses QD274 starter, but uses QD50 starter. It is difficult to start the diesel engine because of lack of power. The pistons, valves and rocker arms of 135 series supercharged and non-supercharged diesel engines are not common, but they are often mixed, which makes it difficult to start the diesel engine, reduce the power and even lead to serious machine parts damage accidents. 1 6 135ZD supercharged diesel engine, due to the wrong use of non-supercharged diesel engine piston, the diesel engine did not start to catch fire after assembly, and the diesel engine started smoothly after replacing the original piston (supercharged type); Different types of diesel engines replace high-pressure oil pipes, nozzle fittings and plunger fittings, which leads to the change of fuel injection quantity and fuel supply advance angle; Substitute defective products for qualified products, iron wires and nails for cotter pins, and steel bars and old bolts for cylindrical pins. The quality cannot be guaranteed and it is absolutely not allowed to be used for a long time. Therefore, in the maintenance of construction machinery, we should try to use the original model of accessories, and we can't replace them with other models, let alone misuse them. Xi' an engineering machinery specialist college
5. Do not pay attention to the selection of bolts, the phenomenon of indiscriminate use of bolts is more prominent.
In the maintenance of construction machinery, the phenomenon of using bolts indiscriminately is still quite prominent. Because the performance and quality of bolts do not meet the technical requirements, mechanical failures often occur after maintenance. Special bolts used in construction machinery, such as transmission shaft bolts, cylinder head bolts, connecting rod bolts, flywheel bolts and fuel injector fixing bolts, are all made of special materials through special processing, with high strength and strong shear resistance, which ensures reliable connection and fixation. In the actual maintenance work, some maintenance personnel found that these bolts were damaged or missing, but they couldn't find the standard bolts at the moment, some took other bolts to replace them at will, and some handled them themselves. These bolts are poor in material or unqualified in processing technology, which leaves hidden dangers for the later use of construction machinery. The six bolts connecting the planetary carrier and the wheel reducer housing in the rear axle of 74 Ⅱ excavator were subjected to great torque, and these six bolts were broken and damaged. Some maintenance personnel often use other bolts or process them by themselves. Some parts need to use small-pitch "fine-thread self-tightening" bolts, copper bolts and copper-plated bolts, but ordinary bolts are used instead, which leads to the phenomenon that the bolts loosen themselves and are not easy to disassemble. For example, the fixing nuts of diesel engine exhaust manifold are mostly copper to prevent heating or long-term use, but ordinary nuts are often used in actual maintenance, which is difficult to remove after a long time; Some bolts will have defects such as stretching and deformation after use. Some technical requirements stipulate that bolts must be replaced after being removed several times. Because the maintenance personnel do not understand these conditions, repeated use of unqualified bolts can easily lead to mechanical failures or accidents. Therefore, in the maintenance of construction machinery, when the bolts are damaged or lost, the bolts that meet the requirements should be replaced in time, and the bolts should not be used indiscriminately.
6. Improper bolt tightening method is more serious. Xi' an engineering machinery specialist college
Most of the fixing or connecting bolts of various parts of construction machinery require tightening torque, such as fuel injector fixing bolts, cylinder head bolts, connecting rod bolts and flywheel bolts. Some specify the tightening torque, some specify the tightening angle, and also specify the tightening sequence. Xi' an engineering machinery specialist college
Some maintenance personnel think it doesn't matter who can tighten the bolts. They don't tighten the bolts according to the specified torque and sequence (some don't know the requirements of tightening torque and sequence at all), don't use a torque (kg) wrench, or use a booster at will to tighten the bolts by feeling, resulting in a great difference in tightening torque. The torque is insufficient, and the bolts are easy to loosen, resulting in the cylinder gasket and bearing bush being washed away, and oil leakage and air leakage; If the torque is too large, the bolt will be easily stretched and deformed, even broken, and sometimes the threaded hole will be damaged, which will affect the repair quality. 1 ZL50 loader, the torque converter throws hydraulic oil outward. After inspection, it was because the 24 bolts connecting the pump wheel and the cover wheel were not tightened in the specified order and torque. Therefore, when maintaining the construction machinery, the bolts must be tightened according to the specified torque and sequence, so as to prevent the machinery from failure due to too large, too small or improper tightening torque. Xi' an engineering machinery specialist college
7. There are quite a few phenomena of not paying attention to detecting the fitting clearance of parts.
Various types of diesel engines have strict requirements on the clearance between piston and cylinder liner, piston ring "three clearances", piston top clearance, valve clearance, plunger clearance, brake shoe clearance, meshing clearance between driving gear and driving gear, axial and radial clearance of bearing, and clearance between valve stem and valve guide. They must be measured during maintenance, and parts that do not meet the clearance requirements should be adjusted or replaced. In the actual maintenance work, there are many phenomena of blindly assembling parts without measuring the fitting clearance, which lead to early wear or ablation of bearings, engine oil burning, difficult starting or deflagration, piston ring fracture, parts collision, oil leakage, and sometimes even serious mechanical damage accidents due to improper fitting clearance. After the overhaul of a 1 diesel engine with a daily output of 6DB- 10P, the commissioning machine will automatically turn off after about 30 minutes, and then the starter will not catch fire. Check whether the oil circuit and oil circuit are normal. After stopping for 30 minutes, you can start the fire again, but it will automatically turn off after running for 30 minutes. Later, the cause of the failure was that the plunger clearance of the fuel injection pump was too small. After the temperature of diesel engine rises, the plunger expands and collides with the oil outlet valve, so it can't supply oil to and from the engine normally and automatically shuts down. After shutdown and cooling, there is a certain gap between the plunger and the oil outlet valve, so the oil can be supplied normally.
8. It is not uncommon to replace a pair or a component in pairs or in sets.
There are many coupling parts on construction machinery, such as plunger pair, oil outlet valve pair and nozzle needle valve pair of diesel fuel system; Driving gear and driven gear in the main reducer of the drive axle; Valve body and valve stem in hydraulic control valve; The valve core and valve sleeve in the full hydraulic steering gear are specially machined and ground in pairs in the factory, and the matching is very precise. During the service life, they are always used in pairs and cannot be interchanged. Some parts that cooperate with each other, such as piston and cylinder liner, bearing bush and journal, valve and valve seat, connecting rod big head tile cover and rod body, have been well matched after a period of running-in. Pay attention to assembly in pairs during maintenance to avoid cross-wiring; Diesel engine connecting rod, piston, fan belt, high-pressure oil pipe, oil seal of excavator central rotary joint, rubber joint of bulldozer main clutch, etc. All of these use a set of accessories at the same time. If it is damaged, it must be replaced in complete sets. Otherwise, the diesel engine is unstable, the hydraulic system leaks oil, the load concentration is serious, and the replaced parts are easy to be damaged prematurely. In the actual maintenance work, some people replace the above parts in pairs or sets in order to reduce the cost, and some people do not understand the technical requirements, which reduces the maintenance quality of construction machinery, shortens the life of parts and increases the possibility of failure. This situation is not uncommon and should be paid enough attention. Xi' an engineering machinery specialist college
9. When assembling, the parts will be turned upside down from time to time.
In the maintenance of construction machinery, some parts have strict direction requirements. Only when installed correctly can the parts work normally. Some parts have no obvious external features, so they can be assembled in front and back. In practical work, parts are often damaged in the early stage, machinery can not work normally, and construction machinery is damaged. Such as engine cylinder gasket, non-equidistant valve spring (such as F6L9 12 diesel engine), engine piston, piston ring, fan blade, gear oil pump side plate, skeleton oil seal, thrust washer, thrust bearing, thrust washer, oil baffle, fuel injection pump plunger, clutch friction plate hub, transmission shaft universal joint, etc. Without knowing the structure and installation precautions, these parts are most likely to be installed backwards, leading to blue smoke in diesel engines, such as 1 4 120F, which may be caused by excessive oil filling or poor matching of piston rings. Xi' an engineering machinery specialist college
Check whether the oil quantity is normal. When the piston connecting rod group of a cylinder is removed, it is found that the piston ring is not "positive", but the gas ring is installed backwards. Check whether the piston rings of other cylinders are also installed in reverse. This machine uses a twisted gas ring with an inner groove. When it is installed, the inner groove is required to face up, but the maintenance personnel just installed it backwards. Because the inner groove piston ring is installed backwards, it is easy for the piston to "pump oil", so that the oil rushes up along the ring mouth and burns in the combustion chamber. Another example is that the working pump of ZL50 loader is equipped with two skeleton oil seals. The correct installation direction of the oil seals is that the inner oil seal lip is inward and the outer oil seal lip is outward, which can prevent the working pump from pumping the oil in the hydraulic oil tank into the gearbox through the variable speed pump, and also prevent the variable speed pump from pumping the oil in the gearbox into the hydraulic oil tank through the working pump (the working pump and the variable speed pump are installed side by side and driven by the shaft gear). I have encountered two cases of oil leakage caused by oil packaging of oil pump. Therefore, when assembling parts, maintenance personnel must master the structure and installation direction requirements of parts, and cannot blindly install them for granted. Xi' an engineering machinery specialist college
10. The maintenance method is not standardized, and "treating the symptoms rather than the root cause" is still the usual means of some maintenance units.
Some maintenance personnel do not adopt correct maintenance methods when maintaining construction machinery, and think that emergency measures are omnipotent. There are still many phenomena that "emergency" replaces "maintenance" and "temporary solution does not cure the root cause". For example, "welding instead of repairing" is often encountered. Some parts could have been repaired, but some maintenance personnel often use the method of "welding to death" to save trouble. 1 set 12V 135 The keyway of the camshaft of the diesel fuel injection pump is worn loose, and the semicircular key is not firmly fixed. It should have been solved by re-milling the keyway, but the maintenance personnel directly welded the camshaft and the connecting plate of the fuel injection pump together, which made it impossible to disassemble and made the later maintenance difficult. After the thread connecting the earrings of the hydraulic cylinder and the piston rod of the hydraulic cylinder is damaged, the oil seal of the hydraulic cylinder cannot be directly welded and replaced, resulting in serious oil leakage; When it is found that the steering of the working device is slow or difficult, the working pressure of the system is raised blindly without checking the cause of the failure, resulting in too high system pressure and easy damage to oil seals, pipelines and hydraulic components. In order to make the diesel engine "energetic", the fuel supply of the fuel injection pump and the fuel injection pressure of the fuel injector are artificially increased. These irregular maintenance methods can only be used in an emergency, not for a long time. It is necessary to find out the cause of the fault fundamentally and take regular maintenance methods to eliminate the fault, which should attract the attention of maintenance personnel. Xi' an engineering machinery specialist college
1 1. The use of gaskets is not standardized, and the phenomenon of indiscriminate use still exists.
There are many kinds of gaskets used between the mating surfaces of construction machinery parts, such as asbestos pads, rubber pads, cardboard pads, cork pads, felt pads, non-ferrous metal pads (copper pads, aluminum pads), copper (steel) asbestos pads, insulation pads, spring pads, flat pads, etc. Some are used to prevent oil leakage, water leakage, air leakage and electric leakage between the mating surfaces of parts, and some are used to tighten and prevent loosening. There are different regulations and requirements for the use time and occasions of each type of gasket. In the maintenance of construction machinery, the phenomenon of irregular use or even indiscriminate use of gaskets is still serious, which often leads to leakage between mating surfaces, loose bolts and nuts, and affects the normal use of construction machinery. The engine cylinder gasket is too thick, the compression ratio is reduced, and it is difficult to start the engine; Copper gasket is used between the matching surface of injector and cylinder head. If asbestos gasket is used instead, it is easy to cause poor heat dissipation and ablation of injector. The gasket on the joint surface between the fuel delivery pump and the fuel injection pump of diesel engine is too thick, which leads to insufficient oil delivery capacity and pressure, and the power of diesel engine decreases; For example, the spring pad, locking pad and gasket are missing, resulting in loose joints or oil leakage; Because there is a hole in the middle of the gasket and the hole is forgotten, the oil and waterway are blocked, and the engine often burns tiles, holds the shaft and boils the water tank. Here, the maintenance personnel are reminded to remember that "the gasket is small, but it is of great use" when maintaining construction machinery. Xi' an engineering machinery specialist college
12. The quality of "small parts" was ignored, and the failure increased because of the loss of "small" and "big".
In the maintenance work, some maintenance personnel often only pay attention to the maintenance of "small parts" such as fuel injection pump, oil transfer pump, piston, cylinder liner, piston ring, hydraulic oil pump, control valve, brake and steering system, while ignoring the maintenance of "small parts" such as filters, overflow valves and various instruments. They think that these "small parts" do not affect the work of machinery, even if they are damaged. As long as the machine moves, they can make do with it. Such as diesel filter, oil filter, air filter, hydraulic oil filter, water temperature gauge, oil temperature gauge, oil pressure gauge, induction plug, sensor, alarm, preheating plug, oil filter screen, water tank cover, oil tank cover, oil filler cap, oil nozzle, air cylinder blowdown switch, storage battery box, fuel injector oil return connector, cotter pin, fan air guide cover, transmission shaft bolt locking piece, etc. These are very important for prolonging the service life of machinery. If you don't pay attention to maintenance during maintenance, you will often lose a lot because of small things, which will lead to the failure of construction machinery. Xi' an engineering machinery specialist college
1 74 type Ⅱ excavator, because the fixing screws of six clutch release arms did not penetrate into the locking pin, 1 the fixing screws fell off and broke during use, resulting in serious damage to the clutch friction plate, release bearing and bearing seat, and the clutch could not work normally. 1 TL 180 bulldozer, the air filter element was damaged and the user failed to replace it in time. When the machine is not used for a long time, the power of the diesel engine drops. It is found that the piston, cylinder, piston ring and valve are seriously worn. The above two failures are due to the neglect of the maintenance of "small parts" and should be taken as a warning. Xi' an engineering machinery specialist college
13. After forgetting the maintenance taboo, hidden faults frequently occur.
When maintaining construction machinery, some maintenance personnel do not understand some problems that should be paid attention to in maintenance, which often leads to "habitual" errors in disassembly and assembly, which affects the quality of machinery maintenance. If the engine cylinder head is disassembled with a hot car, it will easily lead to deformation and cracking of the cylinder head; When installing the piston pin, the piston pin is directly driven into the pin hole without heating the piston, which leads to the deformation and ellipticity of the piston. Adding copper pad or paper pad on the back of crankshaft main bearing pad or connecting rod pad is easy to block the oil path and lead to shaft burning accident; When the diesel engine is repaired, the bearing bush is scraped too much, and the antifriction alloy layer on the surface of the bearing bush is scraped off, which leads to the early wear of the steel back of the bearing bush directly rubbing against the crankshaft; When disassembling interference-fit parts such as bearings and pulleys, the tensioner is not used, and the parts are easily deformed or damaged by hard knocking; When unsealing new parts such as piston, cylinder liner, nozzle coupling and plunger coupling, the oil or wax sealed on the surface of the parts is burned out, which changes the performance of the parts and is not conducive to the use of the parts. Xi' an engineering machinery specialist college
14 parts are not thoroughly decontaminated and cleaned, and early damage and corrosion often occur.
When maintaining construction machinery, it is of great significance to correctly remove oil stains and impurities on the surface of parts to improve maintenance quality and prolong the service life of machinery. Due to careless cleaning of parts, unreasonable selection of cleaning agents and improper cleaning methods, early wear and corrosion damage of parts occur from time to time in some repair units. If carbon deposits on the steps of cylinder liner and piston ring groove, sundries in bolt holes and sand grains in hydraulic components are not completely removed, the torque of bolts is insufficient, the piston ring is easy to break, the cylinder liner is ablated, and the hydraulic components are worn at an early stage. When overhauling construction machinery, if you don't pay attention to removing oil stains or impurities accumulated in diesel filter, oil filter, hydraulic oil filter, diesel water jacket, radiator surface and lubricating oil channel, the maintenance work will be incomplete and the trouble-free running time of construction machinery will be reduced. Maintenance personnel should correctly select cleaning agents when cleaning parts. For the cleaning of various parts, different cleaning agents should be selected correctly according to their different requirements for cleanliness; Secondly, we must prevent parts from corrosion and rust. In order to ensure the quality of parts, corrosion and rust of parts, especially precision parts, should be prevented. Therefore, when cleaning, it is not allowed to use alkaline cleaning agent (especially strong alkali cleaning agent) to clean aluminum alloy parts (such as aluminum alloy cylinder head), and it is not allowed to use strong acid cleaning agent to clean copper parts (such as thermostat main valve) to minimize the corrosion of parts; Third, different parts should be classified and cleaned. Aluminum alloy parts and copper parts should not be cleaned together in alkaline or acidic cleaning agents, and rubber parts should not be cleaned together with other steel parts in gasoline, diesel oil and acid-base cleaning agents. Xi' an engineering machinery specialist college